A middlebox (or network appliance) is a network device that transforms, inspects, filters or otherwise manipulates traffic for various purposes. The middlebox can include, but is not limited to, a firewall, an Intrusion Detection System (“IDS”), a Network Address Translator (“NAT”), a Wide Area Network (“WAN”) optimizer, a load balancer and a WAN virtualizer. The WAN virtualizer enables network managers to use multiple WAN connections to augment or replace individual private WAN connections. WAN virtualization is an end-to-end appliance solution. As such, two WAN virtualizers are needed to provide the multiple WAN connections. These two WAN virtualizers provide a pair of WAN virtualizers connected via different WAN networks. The WAN virtualizers determine the best link to send the high priority packets (traffic) by determining the packet loss, latency, jitter, congestion and other network entities from each of the paths.